EGR (Exhaust Gas Recirculation) systems are employed in automotive vehicles in order to help reduce various engine emissions. Such systems typically employ an EGR valve that is disposed between the engine exhaust manifold and the engine intake manifold, and operable, when in an open position, to re-circulate a portion of the exhaust gases from the exhaust side of the engine back to the intake side. The amount of exhaust gas re-circulation (EGR) is determined by the EGR valve, which is controlled by the engine computer. A typical EGR valve configuration using vacuum control utilizes an electrically actuated vacuum regulator (EVR) and a differential pressure sensor.
High-pressure differential pressure sensors are commonly utilized to monitor fluid and gas pressures such as, for example, petroleum products, hydraulic braking, steam, radiator, air conditioning pump, boiler pressure, and so forth. Pressure sensors typically include a sensor die having a piezoelectric network mounted on a silicon diaphragm that flexes in response to the differential pressure. The sensor die converts the degree of flexing to an electrical signal.
The majority of prior art sensors are based on a single pressure die wherein a topside of the pressure die being exposed to one sensed media and a backside of the pressure die is exposed to a different sensed media. These sensors utilize a common diaphragm, which provides high performance and high accuracy to sense low differential pressures. However, the problem associated with this type of configuration is that the wire bond pads and the topside of the sense die have to be exposed to the sensed media. As a result, the sensed media touches the wirebonds, wirebond pads and the top side of the pressure die which possesses a protective passivation layer to prevent mechanical damage, contamination etc. The sensed media is usually corrosive so that the sensing elements, wirebonds and wirebond pads can be isolated from direct contact with the sensed media for reliable operation.
Some prior art sensors utilize dual pressure die where the sensed media touches only the backside of both pressure die which is very robust with respect to media compatibility, reliability, etc. The problem associated with this configuration is that the sensors utilize two separate pressure diaphragms and the ability to achieve high accuracy of sensing low differential pressures over temperature is limited. Each pressure die exhibits its own unique characteristics such as thermal coefficient of offset and thermal coefficient of gain. Therefore each pressure die provides a unique transfer function and the outputs do not match over temperature, which limits the sensor performance.
Based on the foregoing it is believed that a need exists for an improved unique differential pressure die design for detecting very low differential pressure with respect to a high common mode pressure. It is believed that by utilizing the pressure sensor described in greater detail herein, a low differential pressure can potentially be sensed in a much more efficient and cost-effective manner than prior art devices.